Pancreatic pseudocyst develops as a complication in some cases of pancreatitis. Endoscopic drainage is one of the available therapies, but it has limitations when a visible compression over the gastric or duodenal wall is not present, or when portal hypertension exists. Endoscopic ultrasonography allows for a guided approach even in cases where external compression over the gastrointestinal tract is barely visible or non-existent, and it also helps to prevent vascular injury during puncture of the fluid collection. The most frequent early complications related to cystogastrostomy and cystoduodenostomy are bleeding and pneumoperitoneum, and late complications are stent migration or occlusion, and infection. We report the case of a patient who developed tense pneumoperitoneum immediately after endoscopic ultrasound guided drainage of a pancreatic pseudocyst, and was treated conservatively. This is a severe event, and can be managed by emergency decompression through paracentesis as first line therapy. Most cases of pneumoperitoneum can be managed without surgery, but close observation is mandatory in order to timely detect and treat conditions needing surgical intervention.